The present invention relates to a method for preparing synthetic rubber latex having a large particle size. More particularly, the present invention relates to a method for preparing synthetic rubber latex having a large particle size by adding a synthetic rubber latex as a seed latex to a copolymer latex containing unsaturated acid monomers as an agglomerating agent.
In general, a synthetic rubber latex having a large particle size is used in preparation of high-impact ABS (acrylonitrile-butadiene-styrene) resin, non-glossy ABS resin, foam rubber and so on. Several methods are envisaged to prepare a synthetic rubber latex having a large particle size and these are as follows: (1) regulation of the particle size by controlling the pH value in the polymerization of latex through addition of a base or an acid, (2) addition of an inorganic electrolyte or. an emulsifier during polymerization, (3) agglomeration of the latex by freezing, and (4) mechanical or chemical agglomeration of the synthetic rubber latex particles after polymerization. These methods have been known, however, these methods are disadvantageous, because methods (1) and (2) take a long polymerization time and methods (3) and (4) produce a lot of coagulum.
In order to overcome the shortcomings above, Japanese Patent Publication No.56-45921, and Japanese Patent Laid-open Nos. 58-061102, 59-149902 and U.S. Pat.No. 5,633,304 disclose methods of preparing a synthetic rubber latex having a large particle size by adding an agglomerating agent after completion of polymerization of a synthetic rubber latex. A latex copolymerized with an alkyl acrylate and an unsaturated acid is used as an agglomerating agent. In the other hand, Japanese Patent Laid-open No.59-093701 discloses a latex copolymerized with a conjugated diene monomer and an unsaturated acid as an agglomerating agent.
When a copolymer latex containing unsaturated acid is used as an agglomerating agent as in the Japanese patent applications above, the synthetic rubber latex having a large particle size can be obtained. However, as the stability of the latex deteriorates, coagulum occurs. In case small particle size latex is prepared in a large amount, the latex is not uniform because a bimodal type latex is formed. Such latex cannot be utilized for requiring uniform distribution of the latex.
Accordingly, the present inventors have developed a method of preparing a synthetic rubber latex which has a large particle size, shows good stability and reduces coagulum during polymerization, by controlling the pH value and solid content of the copolymer latex having unsaturated acid which is used for agglomerating a seed latex.
A feature of the present invention is the provision of a method of preparing a synthetic rubber latex that has a large particle size and shows good stability, which comprises controlling the pH value and solid content of the copolymer latex having unsaturated acid which is used as an agglomerating agent.
Another feature of the present invention is the provision of a method of preparing a synthetic rubber latex having a large particle size, showing a uniform distribution, and reducing coagulum by adding a seed synthetic rubber latex with from about 30 to about 55% by weight of solid content and pH value of more than 7.0 as a seed latex to a copolymer latex containing unsaturated acid as an agglomerating agent.
A further feature of the present invention is the provision of a method of preparing a synthetic rubber latex with a large particle size, which is economical due to a shorter preparation time rather than other methods, by adding a seed synthetic rubber latex with from about 30 to about 55% by weight of solid content and pH value of more than 7.0 and with particle sizes from about 500 to about 2000 xc3x85 as a seed latex to a copolymer latex containing unsaturated acid as an agglomerating agent.
The above and other features and advantages of this invention will be apparent from the ensuing disclosure and appended claims.
The present invention provides a method of preparing a synthetic rubber latex having a large particle size, showing good stability and reducing coagulum during polymerization, which comprises (a) pretreating a seed synthetic rubber latex by mixing the seed synthetic rubber latex deionized water and a small amount of an emulsifier and stirring, (b) preparing an agglomerating latex with a pH value of about 5.0xcx9c8.0 by mixing a copolymer latex containing unsaturated acid having from about 10 to about 50% by weight of solid content with deionized water and a pH controlling agent, and (c) adding the pretreated seed synthetic rubber latex of step (a) to the agglomerating latex of step (b). The step (c) may be carried out by adding the pretreated seed synthetic rubber latex dropwisely to the agglomerating latex containing unsaturated acid for about 30 minutes to about 1 hour.